N/A
N/A
The present invention relates generally to electrical isolation between circuit functions in an integrated silicon device. More specifically, the invention relates to the transmission of DC and AC information across a dielectric barrier using a temperature transducer.
Thermocouples are commonly used as temperature sensors. A thermocouple is composed of two touching dissimilar metals forming a sensing junction. When the sensing junction is held at a temperature different from the open ends of the metal, an open-circuit voltage, which is a function of the temperature difference, is created. This thermo-electric voltage is known as the Seebeck voltage. By measuring a thermocouple""s voltage, the temperature can be calculated. When two sensing junctions are connected in series, a differential thermocouple is formed and the open-circuit voltage, Vs is proportional to the temperature difference between the two junctions, Vs=kV(xcex94T), where kV is a millivolts per degree change constant for the particular set of metals used. Thermocouples are traditionally formed as cable assemblies that are strung to temperature generating points remote from the measuring station.
Many applications require electrical isolation between circuit functions. While many methods of performing this electrical isolation exist in discrete circuitry, there are relatively few methods to obtain isolation in an integrated silicon device. For example, differential capacitive and inductive devices encased within the inter-metal dielectric of the die or package have been utilized. These approaches require significant circuitry to process the coupled information. In addition, because these components require time varying signals, direct coupling of DC signals across the isolation barrier is not possible without additional circuit complexity.
A means to isolate circuit functions in an integrated circuit that responds to both AC and DC signals without complex circuitry is desirable.
A differential isolated current comparator achieves isolation using integrated thermo-electric devices and generated thermal gradients. This comparator forms a fundamental cell, which can be scaled for a multitude of new applications. This cell allows for isolation of a measured current, measured voltage or an output voltage from the remainder of the circuitry.
An integrated differential current comparator is formed on a silicon die for providing input to output electrical isolation. The comparator includes a first resistor disposed between a first contact point and a second contact point, the first resistor proximate to the silicon, die. The first resistor generates a first temperature when a first current passes between the first contact point and the second contact point. A second resistor is disposed between a third contact point and a fourth contact point, the second resistor spaced apart from the first resistor and proximate to the silicon die. The second resistor generates a second temperature when a second current passes between the third contact point and the fourth contact point. A thermal difference sensor is disposed on the silicon die. The thermal difference sensor has a first temperature junction thermally coupled to the first resistor and a second temperature junction thermally coupled to the second resistor. The thermal difference sensor provides an output signal that is a function of the temperature difference between the first resistor and the second resistor. Dielectric barriers are interposed between the first temperature junction and the first resistor, and the second temperature junction and the second resistor respectively.
Other aspects, features, and advantages of the present invention are disclosed in the detailed description that follows.